(1) Field of the Invention
This invention relates to a thermal printer of the type in which printing of data is carried out on a sheet of heat-sensitive paper or a sheet of ordinary paper by thermal transfer-ribbon.
(2) Description of the Prior Art
Generally, in thermal printers of the prior art, a thermal head maintained in pressing engagement with a recording sheet is moved in reciprocatory movement along a line of characters being printed as printing data is inputted. Printing is effected either by causing a sheet of heat-sensitive paper serving as a recording sheet to develop a color by letting a multiplicity of heat generating elements of the thermal head generate heat selectively in accordance with the data for one line of characters or melting a coat of thermo-melt ink on a thermal transfer-printing ribbon by the heat generated by the heat generating elements and printing characters on a sheet of ordinary paper serving as a recording sheet. When printing of one line of characters is finished, the thermal head is moved away from the recording sheet; the recording sheet is fed or advanced by one line; and printing of characters on a new line is started. In this way, printing of characters on the recording sheet is carried out successively one line after another.
In the thermal printers of the prior art, difficulties have been experienced in raising the temperature of the thermal head to a sufficiently high level to perform printing satisfactorily. This is because the thermal head is low in temperature prior to initiation of printing or the temperature of the thermal head falls while the line changing operation is being performed. This inevitably results in that the characters printed during initial stages of printing are not well-defined and clear or the quality of the printing characters deteriorates.